One could ask the same thing about any vocation. “Becoming a dentist is all very well but what would happen if everyone became a dentist? There’d be no teachers, no cooks, no taxi drivers.” “Becoming a teacher is all very well but what would happen if everyone became a teacher? There’d be no dentists, etc. etc.” The Buddha did not suggest that everyone should become a monk or nun and indeed that is never going to happen. However, there will always be people who are attracted to the life of simplicity and renunciation and who take delight in the Buddha’s teaching above all else. And like dentists and teachers they have special skills and knowledge that can be helpful to the community in which they live.